Various types of recording paper based on removal of a top cover layer of a metal, typically aluminum, under influence of applied electrical signals, have been proposed.
One such recording carrier is described in German Pat. No. 1 945 939. The outer metal layer is aluminum, applied to a web-like or strip or tape-like paper carrier. The chemical integrity of the metal layer is improved if some proportion of the aluminum of the coating is converted into aluminum oxide or aluminum oxyhydrate. The permanence and stability of the coating are thereby enhanced.
Another way of enhancing the permance and stability of the recording carrier is described in Swiss Pat. No. CH-PS 301 000, in which a metal coating, not further described, is covered with a thin cover coating applied thereover. Such a thin protective cover coating can be obtained by a layer of quartz or paraffin, applied by condensation from a vapor phase. Oils as protective layers in a molecular thickness can also be applied by vapor deposition. It has also been proposed to use a lacquer coating of polystyrene as a protective coating.
It has been proposed to protect optical components such as mirrors, lenses or the like, against chemical and/or mechanical damage by providing a protective layer over the optical elements (see German Patent Disclosure Document DE-OS 22 63 480). Such a protective layer to protect the optical components or devices with respect to mechanical or chemical influences is a hydrophobic protective layer or coating applied to a substrate forming the optical element. The hydrophobic protective layer is obtained by precipitation and polymerization of polysiloxane in an electrical glow discharge. An organo-silicon compound is introduced into a vacuum vessel in the form of a vapor, and polymerized by a glow discharge on the substrate. This protective coating has the advantage of relatively high mechanical hardness and good adhesion, thus providing an improved protective coating with respect to mechanical protection of the substrate while, additionally, having a decreased coefficient of friction with respect to elements or devices sliding thereover, that is, providing for good sliding properties over the thus protected optical component.
The purpose of the protective coating, however made or constituted, is intended to increase the stability and permanence of the actual recording layer. Ideally, the metal recording layer should be protected against decomposition due to ambient humidity or moisture in the air and against abrasion due to travel of the electrodes thereover, which may leave scratches or tracks.